Patchwork [v2,upstream,05/22] add win32 qemu-thread implementation

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Submitter Paolo Bonzini
Date Feb. 26, 2011, 3:40 p.m.
Message ID <1298734819-1960-6-git-send-email-pbonzini@redhat.com>
Download mbox | patch
Permalink /patch/84651/
State New
Headers show

Comments

Paolo Bonzini - Feb. 26, 2011, 3:40 p.m.
For now, qemu_cond_timedwait and qemu_mutex_timedlock are left as
POSIX-only functions.  They can be removed later, once the patches
that remove their uses are in.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 Makefile.objs                        |    4 +-
 qemu-thread.c => qemu-thread-posix.c |    0
 qemu-thread-posix.h                  |   18 +++
 qemu-thread-win32.c                  |  260 ++++++++++++++++++++++++++++++++++
 qemu-thread-win32.h                  |   21 +++
 qemu-thread.h                        |   27 ++--
 6 files changed, 313 insertions(+), 17 deletions(-)
 rename qemu-thread.c => qemu-thread-posix.c (100%)
 create mode 100644 qemu-thread-posix.h
 create mode 100644 qemu-thread-win32.c
 create mode 100644 qemu-thread-win32.h
Blue Swirl - Feb. 26, 2011, 4:47 p.m.
On Sat, Feb 26, 2011 at 5:40 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> For now, qemu_cond_timedwait and qemu_mutex_timedlock are left as
> POSIX-only functions.  They can be removed later, once the patches
> that remove their uses are in.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  Makefile.objs                        |    4 +-
>  qemu-thread.c => qemu-thread-posix.c |    0
>  qemu-thread-posix.h                  |   18 +++
>  qemu-thread-win32.c                  |  260 ++++++++++++++++++++++++++++++++++
>  qemu-thread-win32.h                  |   21 +++
>  qemu-thread.h                        |   27 ++--
>  6 files changed, 313 insertions(+), 17 deletions(-)
>  rename qemu-thread.c => qemu-thread-posix.c (100%)
>  create mode 100644 qemu-thread-posix.h
>  create mode 100644 qemu-thread-win32.c
>  create mode 100644 qemu-thread-win32.h
>
> diff --git a/Makefile.objs b/Makefile.objs
> index 9e98a66..a52f42f 100644
> --- a/Makefile.objs
> +++ b/Makefile.objs
> @@ -142,8 +142,8 @@ endif
>  common-obj-y += $(addprefix ui/, $(ui-obj-y))
>
>  common-obj-y += iov.o acl.o
> -common-obj-$(CONFIG_THREAD) += qemu-thread.o
> -common-obj-$(CONFIG_POSIX) += compatfd.o
> +common-obj-$(CONFIG_POSIX) += qemu-thread-posix.o compatfd.o
> +common-obj-$(CONFIG_WIN32) += qemu-thread-win32.o
>  common-obj-y += notify.o event_notifier.o
>  common-obj-y += qemu-timer.o qemu-timer-common.o
>
> diff --git a/qemu-thread.c b/qemu-thread-posix.c
> similarity index 100%
> rename from qemu-thread.c
> rename to qemu-thread-posix.c
> diff --git a/qemu-thread-posix.h b/qemu-thread-posix.h
> new file mode 100644
> index 0000000..7af371c
> --- /dev/null
> +++ b/qemu-thread-posix.h
> @@ -0,0 +1,18 @@
> +#ifndef __QEMU_THREAD_POSIX_H
> +#define __QEMU_THREAD_POSIX_H 1
> +#include "pthread.h"
> +
> +struct QemuMutex {
> +    pthread_mutex_t lock;
> +};
> +
> +struct QemuCond {
> +    pthread_cond_t cond;
> +};
> +
> +struct QemuThread {
> +    pthread_t thread;
> +};
> +
> +void qemu_thread_signal(QemuThread *thread, int sig);
> +#endif
> diff --git a/qemu-thread-win32.c b/qemu-thread-win32.c
> new file mode 100644
> index 0000000..89422ce
> --- /dev/null
> +++ b/qemu-thread-win32.c
> @@ -0,0 +1,260 @@
> +/*
> + * Win32 implementation for mutex/cond/thread functions
> + *
> + * Copyright Red Hat, Inc. 2010
> + *
> + * Author:
> + *  Paolo Bonzini <pbonzini@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + *
> + */
> +#include "qemu-common.h"
> +#include "qemu-thread.h"
> +#include <process.h>
> +#include <assert.h>
> +#include <limits.h>
> +
> +static void error_exit(int err, const char *msg)
> +{
> +    char *pstr;
> +
> +    FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER,
> +                  NULL, err, 0, (LPTSTR)&pstr, 2, NULL);
> +    fprintf(stderr, "qemu: %s: %s\n", msg, pstr);
> +    LocalFree(pstr);
> +    exit(1);
> +}
> +
> +void qemu_mutex_init(QemuMutex *mutex)
> +{
> +    mutex->owner = 0;
> +    InitializeCriticalSection(&mutex->lock);
> +}
> +
> +void qemu_mutex_lock(QemuMutex *mutex)
> +{
> +    EnterCriticalSection(&mutex->lock);
> +
> +    /* Win32 CRITICAL_SECTIONs are recursive.  Assert that we're not
> +     * using them as such.
> +     */
> +    assert(mutex->owner == 0);
> +    mutex->owner = GetCurrentThreadId();
> +}
> +
> +int qemu_mutex_trylock(QemuMutex *mutex)
> +{
> +    int owned;
> +
> +    owned = TryEnterCriticalSection(&mutex->lock);
> +    if (owned) {
> +        assert(mutex->owner == 0);
> +        mutex->owner = GetCurrentThreadId();
> +    }
> +    return !owned;
> +}
> +
> +void qemu_mutex_unlock(QemuMutex *mutex)
> +{
> +    assert(mutex->owner == GetCurrentThreadId());
> +    mutex->owner = 0;
> +    LeaveCriticalSection(&mutex->lock);
> +}
> +
> +void qemu_cond_init(QemuCond *cond)
> +{
> +    memset(cond, 0, sizeof(*cond));
> +
> +    cond->sema = CreateSemaphore(NULL, 0, LONG_MAX, NULL);
> +    if (!cond->sema) {
> +        error_exit(GetLastError(), __func__);
> +    }
> +    cond->continue_event = CreateEvent(NULL,    /* security */
> +                                       FALSE,   /* auto-reset */
> +                                       FALSE,   /* not signaled */
> +                                       NULL);   /* name */
> +    if (!cond->continue_event) {
> +        error_exit(GetLastError(), __func__);
> +    }
> +}
> +
> +void qemu_cond_signal(QemuCond *cond)
> +{
> +    DWORD result;
> +
> +    /*
> +     * Signal only when there are waiters.  cond->waiters is
> +     * incremented by pthread_cond_wait under the external lock,
> +     * so we are safe about that.
> +     */
> +    if (cond->waiters == 0) {
> +        return;
> +    }
> +
> +    /*
> +     * Waiting threads decrement it outside the external lock, but
> +     * only if another thread is executing pthread_cond_broadcast and
> +     * has the mutex.  So, it also cannot be decremented concurrently
> +     * with this particular access.
> +     */
> +    cond->target = cond->waiters - 1;
> +    result = SignalObjectAndWait(cond->sema, cond->continue_event,
> +                                 INFINITE, FALSE);
> +    if (result == WAIT_ABANDONED || result == WAIT_FAILED) {
> +        error_exit(GetLastError(), __func__);
> +    }
> +}
> +
> +void qemu_cond_broadcast(QemuCond *cond)
> +{
> +    BOOLEAN result;
> +    /*
> +     * As in pthread_cond_signal, access to cond->waiters and
> +     * cond->target is locked via the external mutex.
> +     */
> +    if (cond->waiters == 0) {
> +        return;
> +    }
> +
> +    cond->target = 0;
> +    result = ReleaseSemaphore(cond->sema, cond->waiters, NULL);
> +    if (!result) {
> +        error_exit(GetLastError(), __func__);
> +    }
> +
> +    /*
> +     * At this point all waiters continue. Each one takes its
> +     * slice of the semaphore. Now it's our turn to wait: Since
> +     * the external mutex is held, no thread can leave cond_wait,
> +     * yet. For this reason, we can be sure that no thread gets
> +     * a chance to eat *more* than one slice. OTOH, it means
> +     * that the last waiter must send us a wake-up.
> +     */
> +    WaitForSingleObject(cond->continue_event, INFINITE);
> +}
> +
> +void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
> +{
> +    /*
> +     * This access is protected under the mutex.
> +     */
> +    cond->waiters++;
> +
> +    /*
> +     * Unlock external mutex and wait for signal.
> +     * NOTE: we've held mutex locked long enough to increment
> +     * waiters count above, so there's no problem with
> +     * leaving mutex unlocked before we wait on semaphore.
> +     */
> +    qemu_mutex_unlock(mutex);
> +    WaitForSingleObject(cond->sema, INFINITE);
> +
> +    /* Now waiters must rendez-vous with the signaling thread and
> +     * let it continue.  For cond_broadcast this has heavy contention
> +     * and triggers thundering herd.  So goes life.
> +     *
> +     * Decrease waiters count.  The mutex is not taken, so we have
> +     * to do this atomically.
> +     *
> +     * All waiters contend for the mutex at the end of this function
> +     * until the signaling thread relinquishes it.  To ensure
> +     * each waiter consumes exactly one slice of the semaphore,
> +     * the signaling thread stops until it is told by the last
> +     * waiter that it can go on.
> +     */
> +    if (InterlockedDecrement(&cond->waiters) == cond->target) {
> +        SetEvent(cond->continue_event);
> +    }
> +
> +    qemu_mutex_lock(mutex);
> +}
> +
> +struct qemu_thread_data {

QemuThreadData?
Paolo Bonzini - Feb. 26, 2011, 5:42 p.m.
On 02/26/2011 05:47 PM, Blue Swirl wrote:
> On Sat, Feb 26, 2011 at 5:40 PM, Paolo Bonzini<pbonzini@redhat.com>  wrote:
>> For now, qemu_cond_timedwait and qemu_mutex_timedlock are left as
>> POSIX-only functions.  They can be removed later, once the patches
>> that remove their uses are in.
>>
>> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
>> ---
>>   Makefile.objs                        |    4 +-
>>   qemu-thread.c =>  qemu-thread-posix.c |    0
>>   qemu-thread-posix.h                  |   18 +++
>>   qemu-thread-win32.c                  |  260 ++++++++++++++++++++++++++++++++++
>>   qemu-thread-win32.h                  |   21 +++
>>   qemu-thread.h                        |   27 ++--
>>   6 files changed, 313 insertions(+), 17 deletions(-)
>>   rename qemu-thread.c =>  qemu-thread-posix.c (100%)
>>   create mode 100644 qemu-thread-posix.h
>>   create mode 100644 qemu-thread-win32.c
>>   create mode 100644 qemu-thread-win32.h
>>
>> diff --git a/Makefile.objs b/Makefile.objs
>> index 9e98a66..a52f42f 100644
>> --- a/Makefile.objs
>> +++ b/Makefile.objs
>> @@ -142,8 +142,8 @@ endif
>>   common-obj-y += $(addprefix ui/, $(ui-obj-y))
>>
>>   common-obj-y += iov.o acl.o
>> -common-obj-$(CONFIG_THREAD) += qemu-thread.o
>> -common-obj-$(CONFIG_POSIX) += compatfd.o
>> +common-obj-$(CONFIG_POSIX) += qemu-thread-posix.o compatfd.o
>> +common-obj-$(CONFIG_WIN32) += qemu-thread-win32.o
>>   common-obj-y += notify.o event_notifier.o
>>   common-obj-y += qemu-timer.o qemu-timer-common.o
>>
>> diff --git a/qemu-thread.c b/qemu-thread-posix.c
>> similarity index 100%
>> rename from qemu-thread.c
>> rename to qemu-thread-posix.c
>> diff --git a/qemu-thread-posix.h b/qemu-thread-posix.h
>> new file mode 100644
>> index 0000000..7af371c
>> --- /dev/null
>> +++ b/qemu-thread-posix.h
>> @@ -0,0 +1,18 @@
>> +#ifndef __QEMU_THREAD_POSIX_H
>> +#define __QEMU_THREAD_POSIX_H 1
>> +#include "pthread.h"
>> +
>> +struct QemuMutex {
>> +    pthread_mutex_t lock;
>> +};
>> +
>> +struct QemuCond {
>> +    pthread_cond_t cond;
>> +};
>> +
>> +struct QemuThread {
>> +    pthread_t thread;
>> +};
>> +
>> +void qemu_thread_signal(QemuThread *thread, int sig);
>> +#endif
>> diff --git a/qemu-thread-win32.c b/qemu-thread-win32.c
>> new file mode 100644
>> index 0000000..89422ce
>> --- /dev/null
>> +++ b/qemu-thread-win32.c
>> @@ -0,0 +1,260 @@
>> +/*
>> + * Win32 implementation for mutex/cond/thread functions
>> + *
>> + * Copyright Red Hat, Inc. 2010
>> + *
>> + * Author:
>> + *  Paolo Bonzini<pbonzini@redhat.com>
>> + *
>> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
>> + * See the COPYING file in the top-level directory.
>> + *
>> + */
>> +#include "qemu-common.h"
>> +#include "qemu-thread.h"
>> +#include<process.h>
>> +#include<assert.h>
>> +#include<limits.h>
>> +
>> +static void error_exit(int err, const char *msg)
>> +{
>> +    char *pstr;
>> +
>> +    FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER,
>> +                  NULL, err, 0, (LPTSTR)&pstr, 2, NULL);
>> +    fprintf(stderr, "qemu: %s: %s\n", msg, pstr);
>> +    LocalFree(pstr);
>> +    exit(1);
>> +}
>> +
>> +void qemu_mutex_init(QemuMutex *mutex)
>> +{
>> +    mutex->owner = 0;
>> +    InitializeCriticalSection(&mutex->lock);
>> +}
>> +
>> +void qemu_mutex_lock(QemuMutex *mutex)
>> +{
>> +    EnterCriticalSection(&mutex->lock);
>> +
>> +    /* Win32 CRITICAL_SECTIONs are recursive.  Assert that we're not
>> +     * using them as such.
>> +     */
>> +    assert(mutex->owner == 0);
>> +    mutex->owner = GetCurrentThreadId();
>> +}
>> +
>> +int qemu_mutex_trylock(QemuMutex *mutex)
>> +{
>> +    int owned;
>> +
>> +    owned = TryEnterCriticalSection(&mutex->lock);
>> +    if (owned) {
>> +        assert(mutex->owner == 0);
>> +        mutex->owner = GetCurrentThreadId();
>> +    }
>> +    return !owned;
>> +}
>> +
>> +void qemu_mutex_unlock(QemuMutex *mutex)
>> +{
>> +    assert(mutex->owner == GetCurrentThreadId());
>> +    mutex->owner = 0;
>> +    LeaveCriticalSection(&mutex->lock);
>> +}
>> +
>> +void qemu_cond_init(QemuCond *cond)
>> +{
>> +    memset(cond, 0, sizeof(*cond));
>> +
>> +    cond->sema = CreateSemaphore(NULL, 0, LONG_MAX, NULL);
>> +    if (!cond->sema) {
>> +        error_exit(GetLastError(), __func__);
>> +    }
>> +    cond->continue_event = CreateEvent(NULL,    /* security */
>> +                                       FALSE,   /* auto-reset */
>> +                                       FALSE,   /* not signaled */
>> +                                       NULL);   /* name */
>> +    if (!cond->continue_event) {
>> +        error_exit(GetLastError(), __func__);
>> +    }
>> +}
>> +
>> +void qemu_cond_signal(QemuCond *cond)
>> +{
>> +    DWORD result;
>> +
>> +    /*
>> +     * Signal only when there are waiters.  cond->waiters is
>> +     * incremented by pthread_cond_wait under the external lock,
>> +     * so we are safe about that.
>> +     */
>> +    if (cond->waiters == 0) {
>> +        return;
>> +    }
>> +
>> +    /*
>> +     * Waiting threads decrement it outside the external lock, but
>> +     * only if another thread is executing pthread_cond_broadcast and
>> +     * has the mutex.  So, it also cannot be decremented concurrently
>> +     * with this particular access.
>> +     */
>> +    cond->target = cond->waiters - 1;
>> +    result = SignalObjectAndWait(cond->sema, cond->continue_event,
>> +                                 INFINITE, FALSE);
>> +    if (result == WAIT_ABANDONED || result == WAIT_FAILED) {
>> +        error_exit(GetLastError(), __func__);
>> +    }
>> +}
>> +
>> +void qemu_cond_broadcast(QemuCond *cond)
>> +{
>> +    BOOLEAN result;
>> +    /*
>> +     * As in pthread_cond_signal, access to cond->waiters and
>> +     * cond->target is locked via the external mutex.
>> +     */
>> +    if (cond->waiters == 0) {
>> +        return;
>> +    }
>> +
>> +    cond->target = 0;
>> +    result = ReleaseSemaphore(cond->sema, cond->waiters, NULL);
>> +    if (!result) {
>> +        error_exit(GetLastError(), __func__);
>> +    }
>> +
>> +    /*
>> +     * At this point all waiters continue. Each one takes its
>> +     * slice of the semaphore. Now it's our turn to wait: Since
>> +     * the external mutex is held, no thread can leave cond_wait,
>> +     * yet. For this reason, we can be sure that no thread gets
>> +     * a chance to eat *more* than one slice. OTOH, it means
>> +     * that the last waiter must send us a wake-up.
>> +     */
>> +    WaitForSingleObject(cond->continue_event, INFINITE);
>> +}
>> +
>> +void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
>> +{
>> +    /*
>> +     * This access is protected under the mutex.
>> +     */
>> +    cond->waiters++;
>> +
>> +    /*
>> +     * Unlock external mutex and wait for signal.
>> +     * NOTE: we've held mutex locked long enough to increment
>> +     * waiters count above, so there's no problem with
>> +     * leaving mutex unlocked before we wait on semaphore.
>> +     */
>> +    qemu_mutex_unlock(mutex);
>> +    WaitForSingleObject(cond->sema, INFINITE);
>> +
>> +    /* Now waiters must rendez-vous with the signaling thread and
>> +     * let it continue.  For cond_broadcast this has heavy contention
>> +     * and triggers thundering herd.  So goes life.
>> +     *
>> +     * Decrease waiters count.  The mutex is not taken, so we have
>> +     * to do this atomically.
>> +     *
>> +     * All waiters contend for the mutex at the end of this function
>> +     * until the signaling thread relinquishes it.  To ensure
>> +     * each waiter consumes exactly one slice of the semaphore,
>> +     * the signaling thread stops until it is told by the last
>> +     * waiter that it can go on.
>> +     */
>> +    if (InterlockedDecrement(&cond->waiters) == cond->target) {
>> +        SetEvent(cond->continue_event);
>> +    }
>> +
>> +    qemu_mutex_lock(mutex);
>> +}
>> +
>> +struct qemu_thread_data {
>
> QemuThreadData?

Ok, will resubmit asap.  Can you add this convention to checkpatch?

Paolo

Patch

diff --git a/Makefile.objs b/Makefile.objs
index 9e98a66..a52f42f 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -142,8 +142,8 @@  endif
 common-obj-y += $(addprefix ui/, $(ui-obj-y))
 
 common-obj-y += iov.o acl.o
-common-obj-$(CONFIG_THREAD) += qemu-thread.o
-common-obj-$(CONFIG_POSIX) += compatfd.o
+common-obj-$(CONFIG_POSIX) += qemu-thread-posix.o compatfd.o
+common-obj-$(CONFIG_WIN32) += qemu-thread-win32.o
 common-obj-y += notify.o event_notifier.o
 common-obj-y += qemu-timer.o qemu-timer-common.o
 
diff --git a/qemu-thread.c b/qemu-thread-posix.c
similarity index 100%
rename from qemu-thread.c
rename to qemu-thread-posix.c
diff --git a/qemu-thread-posix.h b/qemu-thread-posix.h
new file mode 100644
index 0000000..7af371c
--- /dev/null
+++ b/qemu-thread-posix.h
@@ -0,0 +1,18 @@ 
+#ifndef __QEMU_THREAD_POSIX_H
+#define __QEMU_THREAD_POSIX_H 1
+#include "pthread.h"
+
+struct QemuMutex {
+    pthread_mutex_t lock;
+};
+
+struct QemuCond {
+    pthread_cond_t cond;
+};
+
+struct QemuThread {
+    pthread_t thread;
+};
+
+void qemu_thread_signal(QemuThread *thread, int sig);
+#endif
diff --git a/qemu-thread-win32.c b/qemu-thread-win32.c
new file mode 100644
index 0000000..89422ce
--- /dev/null
+++ b/qemu-thread-win32.c
@@ -0,0 +1,260 @@ 
+/*
+ * Win32 implementation for mutex/cond/thread functions
+ *
+ * Copyright Red Hat, Inc. 2010
+ *
+ * Author:
+ *  Paolo Bonzini <pbonzini@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+#include "qemu-common.h"
+#include "qemu-thread.h"
+#include <process.h>
+#include <assert.h>
+#include <limits.h>
+
+static void error_exit(int err, const char *msg)
+{
+    char *pstr;
+
+    FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER,
+                  NULL, err, 0, (LPTSTR)&pstr, 2, NULL);
+    fprintf(stderr, "qemu: %s: %s\n", msg, pstr);
+    LocalFree(pstr);
+    exit(1);
+}
+
+void qemu_mutex_init(QemuMutex *mutex)
+{
+    mutex->owner = 0;
+    InitializeCriticalSection(&mutex->lock);
+}
+
+void qemu_mutex_lock(QemuMutex *mutex)
+{
+    EnterCriticalSection(&mutex->lock);
+
+    /* Win32 CRITICAL_SECTIONs are recursive.  Assert that we're not
+     * using them as such.
+     */
+    assert(mutex->owner == 0);
+    mutex->owner = GetCurrentThreadId();
+}
+
+int qemu_mutex_trylock(QemuMutex *mutex)
+{
+    int owned;
+
+    owned = TryEnterCriticalSection(&mutex->lock);
+    if (owned) {
+        assert(mutex->owner == 0);
+        mutex->owner = GetCurrentThreadId();
+    }
+    return !owned;
+}
+
+void qemu_mutex_unlock(QemuMutex *mutex)
+{
+    assert(mutex->owner == GetCurrentThreadId());
+    mutex->owner = 0;
+    LeaveCriticalSection(&mutex->lock);
+}
+
+void qemu_cond_init(QemuCond *cond)
+{
+    memset(cond, 0, sizeof(*cond));
+
+    cond->sema = CreateSemaphore(NULL, 0, LONG_MAX, NULL);
+    if (!cond->sema) {
+        error_exit(GetLastError(), __func__);
+    }
+    cond->continue_event = CreateEvent(NULL,    /* security */
+                                       FALSE,   /* auto-reset */
+                                       FALSE,   /* not signaled */
+                                       NULL);   /* name */
+    if (!cond->continue_event) {
+        error_exit(GetLastError(), __func__);
+    }
+}
+
+void qemu_cond_signal(QemuCond *cond)
+{
+    DWORD result;
+
+    /*
+     * Signal only when there are waiters.  cond->waiters is
+     * incremented by pthread_cond_wait under the external lock,
+     * so we are safe about that.
+     */
+    if (cond->waiters == 0) {
+        return;
+    }
+
+    /*
+     * Waiting threads decrement it outside the external lock, but
+     * only if another thread is executing pthread_cond_broadcast and
+     * has the mutex.  So, it also cannot be decremented concurrently
+     * with this particular access.
+     */
+    cond->target = cond->waiters - 1;
+    result = SignalObjectAndWait(cond->sema, cond->continue_event,
+                                 INFINITE, FALSE);
+    if (result == WAIT_ABANDONED || result == WAIT_FAILED) {
+        error_exit(GetLastError(), __func__);
+    }
+}
+
+void qemu_cond_broadcast(QemuCond *cond)
+{
+    BOOLEAN result;
+    /*
+     * As in pthread_cond_signal, access to cond->waiters and
+     * cond->target is locked via the external mutex.
+     */
+    if (cond->waiters == 0) {
+        return;
+    }
+
+    cond->target = 0;
+    result = ReleaseSemaphore(cond->sema, cond->waiters, NULL);
+    if (!result) {
+        error_exit(GetLastError(), __func__);
+    }
+
+    /*
+     * At this point all waiters continue. Each one takes its
+     * slice of the semaphore. Now it's our turn to wait: Since
+     * the external mutex is held, no thread can leave cond_wait,
+     * yet. For this reason, we can be sure that no thread gets
+     * a chance to eat *more* than one slice. OTOH, it means
+     * that the last waiter must send us a wake-up.
+     */
+    WaitForSingleObject(cond->continue_event, INFINITE);
+}
+
+void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
+{
+    /*
+     * This access is protected under the mutex.
+     */
+    cond->waiters++;
+
+    /*
+     * Unlock external mutex and wait for signal.
+     * NOTE: we've held mutex locked long enough to increment
+     * waiters count above, so there's no problem with
+     * leaving mutex unlocked before we wait on semaphore.
+     */
+    qemu_mutex_unlock(mutex);
+    WaitForSingleObject(cond->sema, INFINITE);
+
+    /* Now waiters must rendez-vous with the signaling thread and
+     * let it continue.  For cond_broadcast this has heavy contention
+     * and triggers thundering herd.  So goes life.
+     *
+     * Decrease waiters count.  The mutex is not taken, so we have
+     * to do this atomically.
+     *
+     * All waiters contend for the mutex at the end of this function
+     * until the signaling thread relinquishes it.  To ensure
+     * each waiter consumes exactly one slice of the semaphore,
+     * the signaling thread stops until it is told by the last
+     * waiter that it can go on.
+     */
+    if (InterlockedDecrement(&cond->waiters) == cond->target) {
+        SetEvent(cond->continue_event);
+    }
+
+    qemu_mutex_lock(mutex);
+}
+
+struct qemu_thread_data {
+    QemuThread *thread;
+    void *(*start_routine)(void *);
+    void *arg;
+};
+
+static int qemu_thread_tls_index = TLS_OUT_OF_INDEXES;
+
+static unsigned __stdcall win32_start_routine(void *arg)
+{
+    struct qemu_thread_data data = *(struct qemu_thread_data *) arg;
+    QemuThread *thread = data.thread;
+
+    free(arg);
+    TlsSetValue(qemu_thread_tls_index, thread);
+
+    /*
+     * Use DuplicateHandle instead of assigning thread->thread in the
+     * creating thread to avoid races.  It's simpler this way than with
+     * synchronization.
+     */
+    DuplicateHandle(GetCurrentProcess(), GetCurrentThread(),
+                    GetCurrentProcess(), &thread->thread,
+                    0, FALSE, DUPLICATE_SAME_ACCESS);
+
+    qemu_thread_exit(data.start_routine(data.arg));
+    abort();
+}
+
+void qemu_thread_exit(void *arg)
+{
+    QemuThread *thread = TlsGetValue(qemu_thread_tls_index);
+    thread->ret = arg;
+    CloseHandle(thread->thread);
+    thread->thread = NULL;
+    ExitThread(0);
+}
+
+static inline void qemu_thread_init(void)
+{
+    if (qemu_thread_tls_index == TLS_OUT_OF_INDEXES) {
+        qemu_thread_tls_index = TlsAlloc();
+        if (qemu_thread_tls_index == TLS_OUT_OF_INDEXES) {
+            error_exit(ERROR_NO_SYSTEM_RESOURCES, __func__);
+        }
+    }
+}
+
+
+void qemu_thread_create(QemuThread *thread,
+                       void *(*start_routine)(void *),
+                       void *arg)
+{
+    HANDLE hThread;
+
+    struct qemu_thread_data *data;
+    qemu_thread_init();
+    data = qemu_malloc(sizeof *data);
+    data->thread = thread;
+    data->start_routine = start_routine;
+    data->arg = arg;
+
+    hThread = (HANDLE) _beginthreadex(NULL, 0, win32_start_routine,
+                                      data, 0, NULL);
+    if (!hThread) {
+        error_exit(GetLastError(), __func__);
+    }
+    CloseHandle(hThread);
+}
+
+void qemu_thread_get_self(QemuThread *thread)
+{
+    if (!thread->thread) {
+        /* In the main thread of the process.  Initialize the QemuThread
+           pointer in TLS, and use the dummy GetCurrentThread handle as
+           the identifier for qemu_thread_is_self.  */
+        qemu_thread_init();
+        TlsSetValue(qemu_thread_tls_index, thread);
+        thread->thread = GetCurrentThread();
+    }
+}
+
+int qemu_thread_is_self(QemuThread *thread)
+{
+    QemuThread *this_thread = TlsGetValue(qemu_thread_tls_index);
+    return this_thread->thread == thread->thread;
+}
diff --git a/qemu-thread-win32.h b/qemu-thread-win32.h
new file mode 100644
index 0000000..878f86a
--- /dev/null
+++ b/qemu-thread-win32.h
@@ -0,0 +1,21 @@ 
+#ifndef __QEMU_THREAD_WIN32_H
+#define __QEMU_THREAD_WIN32_H 1
+#include "windows.h"
+
+struct QemuMutex {
+    CRITICAL_SECTION lock;
+    LONG owner;
+};
+
+struct QemuCond {
+    LONG waiters, target;
+    HANDLE sema;
+    HANDLE continue_event;
+};
+
+struct QemuThread {
+    HANDLE thread;
+    void *ret;
+};
+
+#endif
diff --git a/qemu-thread.h b/qemu-thread.h
index add97bf..acdb6b2 100644
--- a/qemu-thread.h
+++ b/qemu-thread.h
@@ -1,24 +1,16 @@ 
 #ifndef __QEMU_THREAD_H
 #define __QEMU_THREAD_H 1
-#include "semaphore.h"
-#include "pthread.h"
-
-struct QemuMutex {
-    pthread_mutex_t lock;
-};
-
-struct QemuCond {
-    pthread_cond_t cond;
-};
-
-struct QemuThread {
-    pthread_t thread;
-};
 
 typedef struct QemuMutex QemuMutex;
 typedef struct QemuCond QemuCond;
 typedef struct QemuThread QemuThread;
 
+#ifdef _WIN32
+#include "qemu-thread-win32.h"
+#else
+#include "qemu-thread-posix.h"
+#endif
+
 void qemu_mutex_init(QemuMutex *mutex);
 void qemu_mutex_destroy(QemuMutex *mutex);
 void qemu_mutex_lock(QemuMutex *mutex);
@@ -28,6 +20,12 @@  void qemu_mutex_unlock(QemuMutex *mutex);
 
 void qemu_cond_init(QemuCond *cond);
 void qemu_cond_destroy(QemuCond *cond);
+
+/*
+ * IMPORTANT: The implementation does not guarantee that pthread_cond_signal
+ * and pthread_cond_broadcast can be called except while the same mutex is
+ * held as in the corresponding pthread_cond_wait calls!
+ */
 void qemu_cond_signal(QemuCond *cond);
 void qemu_cond_broadcast(QemuCond *cond);
 void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex);
@@ -36,7 +34,6 @@  int qemu_cond_timedwait(QemuCond *cond, QemuMutex *mutex, uint64_t msecs);
 void qemu_thread_create(QemuThread *thread,
                        void *(*start_routine)(void*),
                        void *arg);
-void qemu_thread_signal(QemuThread *thread, int sig);
 void qemu_thread_get_self(QemuThread *thread);
 int qemu_thread_is_self(QemuThread *thread);
 void qemu_thread_exit(void *retval);